Pollination: The Mystery of Attraction

Darwin suspected that insects must have been a major diversifying force in the evolution of flowering plants. Fossil evidence uncovered since his time supports that claim. Today, the earth has more than 250,000 species of flowering plants – and only about 1,000 species of wind-pollinated conifers.

Victorians already knew that moths flock to the exquisitely sweet-scented Night-Blooming Cereus. The wealthy sometimes hosted nighttime parties to await its one-night-only blossoming. Darwin studied how moths feed on the nectar of this cactus and then carry pollen to another flower.

Only large bumblebees pollinate the foxglove (Digitalis). Sturdy hairs adorning the colored spots on the flower’s corolla both prevent smaller insects from entering and collect pollen that transfers to the bee’s underside upon entry. The two upper (longer) stamens may also shed pollen on the bee’s back.

Color print by Elsa Felsko, 1954.

Darwin studied morning glories (Ipomoea purpurea) for eleven years. He noticed that offspring of cross-pollinated plants consistently out-performed those of self-pollinated plants in terms of size and number of seeds.